Cylinder operation control apparatus for internal combustion engine

ABSTRACT

A cylinder operation control apparatus includes: an internal combustion engine (E) which is adapted to operate in an all-cylinder activation mode and in a cylinder deactivation mode; a lift amount changing device (VT) which is associated with the internal combustion engine (E), and which enables switching between the all-cylinder activation mode and the cylinder deactivation mode by changing the amount of lifts of intake and exhaust valves (IV, EV) associated with the cylinders; a lift operating device ( 33 ) which is associated with the lift amount changing device (VT) to operate the same; a cylinder activation enforcing device ( 33 ′) which is operatively disposed between the lift amount changing device (VT) and the lift operating device ( 33 ) so as to enforce the all-cylinder activation mode as necessary.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cylinder operation control apparatusfor an internal combustion engine, which enables a switching operationbetween an all-cylinder activation mode in which all cylinders of theengine are activated, and a cylinder deactivation mode in which at leasta cylinder of the engine is deactivated.

2. Description of the Related Art

Among hybrid vehicles, a type of hybrid vehicle is known in which acylinder deactivation operation is executed, for example, by controllingvalve trains of the engine using hydraulic control method in order tofurther improve fuel economy by means of reduction in friction of theengine. In this type of hybrid vehicle, when the vehicle enters adeceleration state, a cylinder deactivation operation is executed alongwith a fuel cut operation so as to decrease engine friction, and as aresult, the amount of regenerated electric energy is increased by anamount corresponding to the decreased engine friction, and thus fueleconomy is improved (see, for example, Japanese Unexamined PatentApplication, First Publication No. Hei 07-63097).

Accordingly, if an engine is employed, in which an all-cylinderdeactivation operation is made possible, energy, which would have beendissipated due to engine friction during a deceleration operation, canbe maximally recovered, and thus a hybrid vehicle having excellent fueleconomy can be obtained.

As described above, fuel economy can be greatly improved by employing anall-cylinder deactivation operation; however, in general, some of thecylinders must remain as normally activated cylinders so as to be ableto drive the vehicle upon resuming fuel supply to the activatedcylinders just in case the cylinder deactivation mechanism fails.Accordingly, friction due to the normally activated cylinders remainunchanged during a deceleration operation; therefore, fuel economy isnot greatly improved.

SUMMARY OF THE INVENTION

In view of the above circumstances, an object of the present inventionis to provide a cylinder operation control apparatus for an internalcombustion engine, which enables maximal improvement in fuel economy dueto a cylinder deactivation operation, while also enabling drive of thevehicle even when a valve lift operating device in a cylinderdeactivation mechanism fails.

In order to achieve the above object, the present invention provides acylinder operation control apparatus including: an internal combustionengine which is adapted to operate in an all-cylinder activation mode inwhich all-cylinders thereof are activated, and in a cylinderdeactivation mode in which at least a cylinder thereof is deactivated; alift amount changing device which is associated with the internalcombustion engine, and which enables switching between the all-cylinderactivation mode and the cylinder deactivation mode by changing theamount of lifts of intake and exhaust valves associated with thecylinders; a lift operating device which is associated with the liftamount changing device to operate the same; a cylinder activationenforcing device which is operatively disposed between the lift amountchanging device and the lift operating device so as to enforce theall-cylinder activation mode as necessary; and a control unit which isoperatively connected to the lift amount changing device, the liftoperating device, and the cylinder activation enforcing device, forcontrolling the operation mode of the internal combustion engine.

According to the above cylinder operation control apparatus of thepresent invention, the internal combustion engine can be placed in theall-cylinder activation mode or in the cylinder deactivation mode byoperating the lift amount changing device using the lift operatingdevice so as to control the amount of lifts of the intake and exhaustvalves. In addition, the internal combustion engine can be enforcedlyreturned to the all-cylinder activation mode from the cylinderdeactivation mode by operating the cylinder activation enforcing device;therefore, the internal combustion engine can be reliably returned tothe all-cylinder activation mode from a state in which all of thecylinders are deactivated.

In the above cylinder operation control apparatus, the lift amountchanging device may include a hydraulic variable valve timing mechanism.The control unit may be adapted to control the oil pressure for thehydraulic variable valve timing mechanism so as to suspend theoperations of the intake and exhaust valves when the internal combustionengine is placed in the cylinder deactivation mode. The control unit maybe adapted to operate the cylinder activation enforcing device so as toenforce normal operations of the intake and exhaust valves as necessary.

According to the above cylinder operation control apparatus of thepresent invention, by suspending the operations of the intake andexhaust valves using the hydraulic variable valve timing mechanism, theengine friction can be further reduced, and fuel economy can also befurther improved.

The present invention also provides a cylinder operation controlapparatus including: an internal combustion engine which is adapted tooperate in an all-cylinder activation mode in which all-cylindersthereof are activated, and in a cylinder deactivation mode in which atleast a cylinder thereof is deactivated; a lift amount changing devicewhich is associated with the internal combustion engine, and which isadapted to change the amount of lifts of intake and exhaust valvesassociated with the cylinders using an operation oil supplied from ahydraulic power source; a cylinder activation passage connected to thelift amount changing device for placing the internal combustion enginein the all-cylinder activation mode; a cylinder deactivation passageconnected to the lift amount changing device for placing the internalcombustion engine in the cylinder deactivation mode; an oil supplypassage which is connected to the cylinder activation passage and thecylinder deactivation passage for supplying the operation oil to thelift amount changing device, and which is provided with an oil supplybranching passage branching therefrom; a drain passage which isconnected to the cylinder activation passage and the cylinderdeactivation passage for allowing the operation oil to return to thehydraulic power source, and which is provided with a drain branchingpassage branching therefrom; a switching device which is connected tothe cylinder activation passage, the cylinder deactivation passage, theoil supply passage, and the drain passage, for optionally supplying theoperation oil from the hydraulic power source to the cylinder activationpassage or to the cylinder deactivation passage; and a cylinderactivation enforcing device which is connected to the cylinderactivation passage, the cylinder deactivation passage, the oil supplybranching passage, and the drain branching passage, for enforcing theall-cylinder activation mode.

In the above cylinder operation control apparatus, the cylinderactivation enforcing device may include: a cylinder activation port foroptionally connecting the oil supply branching passage to the cylinderactivation passage or disconnecting the oil supply branching passagefrom the cylinder activation passage; and a cylinder deactivation portfor optionally connecting the drain branching passage to the cylinderdeactivation passage or disconnecting the drain branching passage fromthe cylinder deactivation passage.

According to the above cylinder operation control apparatus of thepresent invention, the operation mode of the internal combustion enginecan be switched between the all-cylinder activation mode and thecylinder deactivation mode by optionally supplying the operation oilfrom the hydraulic power source to the cylinder activation passage or tothe cylinder deactivation passage using the switching device. Moreover,the operation oil can be supplied to the cylinder activation passage soas to place the engine in the all-cylinder activation mode by connectingthe oil supply branching passage to the cylinder activation passageusing the cylinder activation port of the cylinder activation enforcingdevice and by connecting the drain branching passage to the cylinderdeactivation passage using the cylinder deactivation port even when theengine is supposed to be placed in the cylinder deactivation mode inwhich the operation oil is supplied to the cylinder deactivation passageby the operation of the switching device. Therefore, the internalcombustion engine can be reliably returned to the all-cylinderactivation mode from a state in which all of the cylinders aredeactivated.

In the above cylinder operation control apparatus, the cylinderactivation enforcing device may include a spool valve having a spooltherein. The spool valve may be adapted to perform the connecting anddisconnecting operations between the oil supply branching passage andthe cylinder activation passage, and connecting and disconnectingoperations between the drain branching passage and the cylinderdeactivation passage, by sliding the spool to respective predeterminedpositions.

According to the above cylinder operation control apparatus of thepresent invention, the connection or disconnection between the supplybranching passage and the cylinder activation passage, and theconnection or disconnection between the drain branching passage and thecylinder deactivation passage can be performed by the cylinderactivation port and the cylinder deactivation port, i.e., the connectionor disconnection between the supply branching passage and the cylinderactivation passage, and the connection or disconnection between thedrain branching passage and the cylinder deactivation passage can beexecuted by just a single operation of the spool; therefore, apreferable efficiency in operation can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the general structure of a hybridvehicle in a first embodiment according to the present invention.

FIG. 2 is a front view showing a variable valve timing mechanism used inthe first embodiment of the present invention.

FIGS. 3A and 3B show the variable valve timing mechanism used in thefirst embodiment of the present invention; in particular, FIG. 3A showsa cross-section of the main part of the variable valve timing mechanismin an all-cylinder activation mode, and FIG. 3B shows a cross-section ofthe main part of the variable valve timing mechanism in an all-cylinderdeactivation mode.

FIG. 4 is an enlarged view of the main part in FIG. 1.

FIG. 5 is a diagram showing the flow of an operation oil in theall-cylinder activation mode.

FIG. 6 is a diagram showing the flow of the operation oil in theall-cylinder deactivation mode.

FIG. 7 is a diagram showing the flow of the operation oil in a state inwhich a spool valve 33 is switched into the all-cylinder deactivationmode, but the operation mode is in the all-cylinder activation mode dueto operation of another spool valve 33′.

FIG. 8 is a plan view showing a spool valve 70′ as a second embodimentof the present invention.

FIG. 9A is a cross-sectional view showing the spool valve 70′ in FIG. 8taken along the line A-A, and FIG. 9B is a cross-sectional view showingthe spool valve 70′ in FIG. 8 taken along the line B-B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be explainedbelow with reference to the appended drawings.

The construction of a parallel hybrid vehicle, which includes ahydraulic pressure supplying device for valve trains according to afirst embodiment of the present invention, will be explained below withreference to FIG. 1.

As shown in FIG. 1, the hybrid vehicle includes an engine E, a motor M,and a transmission T, which are coupled to each other in series. Thedriving power generated by at least one of the engine E and the motor Mis transmitted via, for example, a CVT (continuously variabletransmission) as the transmission T (the transmission T may be a manualtransmission) to front wheels Wf as driving wheels. When the drivingpower is transmitted from the driving wheels Wf to the motor M duringdeceleration of the hybrid vehicle, the motor M acts as a generator forapplying a so-called regenerative braking force to the vehicle, i.e.,the kinetic energy of the vehicle is recovered and stored as electricalenergy.

The driving of the motor M and the regenerating operation of the motor Mare controlled by a power drive unit (PDU) 2 according to controlcommands from a motor CPU 1M of a motor ECU 1. A high-voltage nickelmetal hydride battery 3 for sending electrical energy to and receivingelectrical energy from the motor M is connected to the power drive unit2. The battery 3 includes a plurality of modules connected in series,and in each module, a plurality of cell units are connected in series.The hybrid vehicle includes a 12-volt auxiliary battery 4 for energizingvarious electrical accessories. The auxiliary battery 4 is connected tothe battery 3 via a downverter 5 as a DC-DC converter. The downverter 5,which is controlled by an FIECU 11, makes the voltage from the battery 3step-down and charges the auxiliary battery 4. Note that the motor ECU 1includes a battery CPU 1B for protecting the battery 3 and calculatingthe state of charge of the battery 3. In addition, a CVTECU 21 isconnected to the transmission T, which is a CVT, for controlling thesame.

The FIECU 11 controls, in addition to the motor ECU 1 and the downverter5, a fuel injection valve (not shown) for controlling the amount of fuelsupplied to the engine E, a starter motor, ignition timing, etc. To thisend, the FIECU 11 receives various signals such as a signal from avehicle speed sensor, a signal from an engine revolution rate sensor, asignal from a shift position sensor, a signal from a brake switch, asignal from a clutch switch, a signal from a throttle opening-degreesensor, and a signal from an intake negative pressure sensor. Inaddition, the FIECU 11 also receives a signal from POIL sensor (oilpressure measuring device) S1, and signals from the solenoids of spoolvalves 33 and 33′, which will be further explained later.

Next, the variable valve timing mechanism VT and hydraulic controldevices therefor will be explained in detail with reference to FIGS. 2to 4.

As shown in FIG. 2, the cylinder (not shown) is provided with an intakevalve IV and an exhaust valve EV which are biased by valve springs 51and 51 in a direction which closes an intake port (not shown) and anexhaust port (not shown), respectively. Reference symbol 52 indicates alift cam provided on a camshaft 53. The lift cam 52 is engaged with anintake cam lifting rocker arm 54 a for lifting the intake valve and anexhaust cam lifting rocker arm 54 b for lifting the exhaust valve, bothof which are rockably supported by the rocker shaft 31.

The rocker shaft 31 also supports valve operating rocker arms 55 a and55 b in a rockable manner, which are located adjacent to the cam liftingrocker arms 54 a and 54 b, and whose rocking ends press the top ends ofthe intake valve IV and the exhaust valve EV, respectively, so that theintake valve IV and the exhaust valve EV open their respective ports. Asshown in FIGS. 3A and 3B, the proximal ends (opposite the endscontacting the valves) of the valve operating rocker arms 55 a and 55 bare adapted to engage a circular cam 531 provided on the camshaft 53.

FIGS. 3A and 3B show, as an example, the cam lifting rocker arm 54 b andthe valve operating rocker arm 55 b associated with the exhaust valveEV.

As shown in FIGS. 3A and 3B, a hydraulic chamber 56 is formed in the camlifting rocker arm 54 b and the valve operating rocker arm 55 b in acontinuous manner, which is located on the opposite side of the rockershaft 31 with respect to the lift cam 52. The hydraulic chamber 56 isprovided with a pin 57 a and a disengaging pin 57 b, both of which aremade slidable and are biased toward the cam lifting rocker arm 54 b bymeans of a pin spring 58.

The rocker shaft 31 is provided therein a hydraulic passage 59 which isdivided into hydraulic passages 59 a and 59 b by a partition S. Thehydraulic passage 59 b is connected to the hydraulic chamber 56 at theposition where the disengaging pin 57 b is located via an opening 60 bof the hydraulic passage 59 b and a communication port 61 b in the camlifting rocker arm 54 b. The hydraulic passage 59 a is connected to thehydraulic chamber 56 at the position where the pin 57 a is located viaan opening 60 a of the hydraulic passage 59 a and a communication port61 a in the valve operating rocker arm 55 b, and is adapted to befurther connectable to a drain passage 38.

As shown in FIG. 3A, the pin 57 a is positioned by the pin spring 58 soas to bridge the cam lifting rocker arm 54 b and the valve operatingrocker arm 55 b when oil pressure is not applied via the hydraulicpassage 59 b. On the other hand, when oil pressure is applied via thehydraulic passage 59 b in accordance with a cylinder deactivationsignal, both of the pin 57 a and the disengaging pin 57 b slide towardthe valve operating rocker arm 55 b against the biasing force of the pinspring 58, and the interface between the pin 57 a and the disengagingpin 57 b corresponds to the interface between the cam lifting rocker arm54 b and the valve operating rocker arm 55 b so as to disconnect theserocker arms 54 b and 55 b, as shown in FIG. 3B. The intake valve side isconstructed in a similar manner. The hydraulic passages 59 a and 59 bare connected to an oil pump 32 via the spool valves 33 and 33′ whichare provided for ensuring oil pressure of the variable valve timingmechanisms VT.

As shown in FIG. 4, a cylinder deactivation passage 34 is connected tothe hydraulic passage 59 b in the rocker shaft 31, and a cylinderactivation passage 35 is connected to the hydraulic passage 59 a.

The spool valve 33′, which is provided as a cylinder activationenforcing device, is disposed between the spool valve 33, which isprovided as a lift amount changing device, and the variable valve timingmechanisms VT, which are provided as a lift operating device. Acontinuous cylinder activation, which will be explained below in detail,is executed by operating the spool valve 33′.

As shown in FIG. 5, the spool valve 33 includes a casing 45 in whichconnection ports H1 to H4 are formed, and a spool 43 disposed inside thecasing 45. In the surface of the spool 43 that faces the inner surfaceof the casing 45 in which connection ports H1 to H4 are formed, thereare formed recesses, and the recesses and the inner surface of thecasing 45 delimit ports P1 to P4. Among the ports P1 to P4, the ports P1and P4 are connected to each other via a communication passage 44. Thespool 43 is made slidable along the inner surface of the casing 45 inwhich connection ports H1 to H4 are formed using a solenoid (not shown).

Moreover, similarly to the spool valve 33, the spool valve 33′ includesa casing 45′ in which connection ports H1′ to H6′ are formed, and aspool 43′ disposed inside the casing 45′. Recesses, which are formed inthe spool 43′, and the inner surface of the casing 45′ of the spool 43′delimit ports P1′ to P7′. The spool 43′ is made slidable along the innersurface of the casing 45′ using a solenoid (not shown).

The connection ports H1 to H4 of the spool valve 33 and the connectionports H1′ to H6′ of the spool valve 33′ are connected to oil passages inwhich the operation oil flows, respectively. More specifically, theconnection ports H1 to H4 are connected to a drain passage 38, acylinder activation connection passage 42, an oil supply passage 36, anda cylinder deactivation connection passage 41, respectively. Theconnection ports H1′ to H6′ are connected to a drain branching passage38′ (a branching passage 38′), the cylinder deactivation passage 34, thecylinder deactivation connection passage 41, an oil supply branchingpassage 36′ (a branching passage 36′), the cylinder activation passage35, the cylinder activation connection passage 42, respectively.

When the spool 43 of the spool valve 33 and the spool 43′ of the spoolvalve 33′ are slid, the above-mentioned passages are connected to eachother and disconnected from each other by means of the ports P1 to P4formed in the spool 43 and the ports P1′ to P7′ formed in the spool 43′.Such operations will be further explained below with reference to FIGS.5 to 7.

FIG. 5 is a diagram showing the flow of the operation oil in theall-cylinder activation mode. As shown in FIG. 5, the spool valve 33 iscontrolled so that the drain passage 38 and the cylinder deactivationconnection passage 41 are connected to each other via the ports P1 andP4, and the oil supply passage 36 and the cylinder activation connectionpassage 42 are connected to each other via the ports P2 and P3. On theother hand, the spool valve 33′ is controlled so that the cylinderdeactivation passage 34 and the cylinder deactivation connection passage41 are connected to each other via the port P4′, the cylinder activationconnection passage 42 and the cylinder activation passage 35 areconnected to each other via the port P7′, and the branching passages 38′and 36′ are closed by the ports P2′ and P5′.

In this state, the operation oil supplied from the oil pump 32 (see FIG.4) flows into the connection port H3 of the spool valve 33 via the oilsupply passage 36, and then flows into the cylinder activationconnection passage 42 via the port P3 and the connection port H2. Theoperation oil which flowed into the cylinder activation connectionpassage 42 flows into the connection port H6′ in the spool valve 33′,and flows into the cylinder activation passage 35 via the port P7′ andthe connection port H5′, and thus the operation oil is supplied into theoil passage 59 a in the rocker shaft 31. The branching passage 36′branching from the oil supply passage 36 is closed by the port P5′.

On the other hand, the operation oil that has been held in the oilpassage 59 b in the rocker shaft 31 flows into the connection port H2′in the spool valve 33′ via the cylinder deactivation passage 34, andthen flows into the cylinder deactivation connection passage 41 via theport P4′ and the connection port H3′. The operation oil which flowedinto the cylinder deactivation connection passage 41 flows into theconnection port H4 in the spool valve 33, and then flows into the drainpassage 38 via the port P4, the communication passage 44, the port P1,and the connection port H1. The branching passage 38′ branching from thedrain passage 38 is closed by the port P2′.

As explained above, the operation oil is supplied into the hydraulicpassage 59 a for the all-cylinder activation operation provided in therocker shaft 31, and the operation oil that has been held in thehydraulic passage 59 b for the all-cylinder deactivation operation isreleased, and thus the all-cylinder activation operation is executed.

FIG. 6 is a diagram showing the flow of the operation oil in theall-cylinder deactivation mode. As shown in FIG. 6, the spool 43 of thespool valve 33 is moved downward when compared with the state shown inFIG. 5. As shown in FIG. 6, the spool valve 33 is controlled so that thedrain passage 38 and the cylinder activation connection passage 42 areconnected to each other via the ports P1 and P2, and the oil supplypassage 36 and the cylinder deactivation connection passage 41 areconnected to each other via the port P3.

On the other hand, the spool 43′ of the spool valve 33′ is held in thesame position as in the state shown in FIG. 5.

In this state, the operation oil supplied from the oil pump 32 (see FIG.4) flows into the connection port H3 of the spool valve 33 via the oilsupply passage 36, and then flows into the cylinder deactivationconnection passage 41 via the port P3 and the connection port H4. Theoperation oil which flowed into the cylinder deactivation connectionpassage 41 flows into the connection port H3′ in the spool valve 33′,and flows into the cylinder deactivation passage 34 via the port P4′ andthe connection port H2′, and thus the operation oil is supplied into theoil passage 59 b in the rocker shaft 31. The branching passage 36′branching from the oil supply passage 36 is closed by the port P5′ as inthe state shown in FIG. 5.

On the other hand, the operation oil that has been held in the oilpassage 59 a in the rocker shaft 31 flows into the connection port H5′in the spool valve 33′ via the cylinder activation passage 35, and thenflows into the cylinder activation connection passage 42 via the portP7′ and the connection port H6′. The operation oil which flowed into thecylinder activation connection passage 42 flows into the connection portH2 in the spool valve 33, and then flows into the drain passage 38 viathe port P1 and the connection port H1. The branching passage 38′branching from the drain passage 38 is closed by the port P2′.

As explained above, the operation oil is supplied into the hydraulicpassage 59 b for the all-cylinder deactivation operation provided in therocker shaft 31, and the operation oil that has been held in thehydraulic passage 59 a for the all-cylinder activation operation isreleased, and thus the all-cylinder deactivation operation is executed.

In contrast, when the spool 43 of the spool valve 33 is fixed in theposition shown in FIG. 6 due to defectiveness, the spool valve 33′ isoperated as shown in FIG. 7.

FIG. 7 is a diagram showing the flow of the operation oil in theall-cylinder activation mode which is enforced by the spool valve 33′even though the spool valve 33 is switched into the all-cylinderdeactivation mode. As shown in FIG. 7, the spool 43′ of the spool valve33′ is moved downward when compared with the state shown in FIG. 6. Asshown in FIG. 7, the spool valve 33′ is controlled so that the drainbranching passage 38′ and the cylinder deactivation passage 34 areconnected to each other via the port P2′, and drain branching passage38′ and the cylinder activation passage 35 are connected to each othervia the port P5′. The cylinder deactivation passage 34 and the cylinderdeactivation connection passage 41 are disconnected from each other bythe port P4′. The cylinder activation connection passage 42 and thecylinder activation passage 35 are disconnected from each other by theport P7′.

Accordingly, as shown in FIG. 7, the operation oil supplied from the oilpump 32 (see FIG. 4) flows into the connection port H4′ of the spoolvalve 33′ via the branching passage 36′, and then flows into thecylinder activation passage 35 via the port P5′ and the connection portH5′, and thus the operation oil is supplied into the oil passage 59 a inthe rocker shaft 31. On the other hand, the operation oil that has beenheld in the oil passage 59 b in the rocker shaft 31 flows into theconnection port H2′ in the spool valve 33′ via the cylinder deactivationpassage 34, and then flows into the drain branching passage 38′ via theport P2′ and the connection port H1′. The flow of the operation oil fromthe cylinder deactivation passage 34 into the cylinder deactivationconnection passage 41 is blocked by the port P4′, and the flow of theoperation oil from the cylinder activation passage 35 into the drainpassage 38 via the cylinder activation connection passage 42 is blockedby the port P7′.

As explained above, even when the spool 43 of the spool valve 33 isfixed in the position shown in FIG. 6 due to defectiveness, the engine Ecan be reliably placed in or returned to the all-cylinder activationmode by operating the spool 43′ of the spool valve 33′.

According to the present embodiment, the connection or disconnectionbetween the supply branching passage 36′ and the cylinder activationpassage 35, and the connection or disconnection between the drainbranching passage 38′ and the cylinder deactivation passage 34 can beexecuted by a single operation of the spool 43′ of the spool valve 33′;therefore, a preferable efficiency in operation can be obtained.

Next, a second embodiment of the present invention will be explainedbelow with reference to FIG. 8. FIG. 8 is a plan view showing a spoolvalve 70′ according to the second embodiment. FIG. 9A is across-sectional view showing the spool valve 70′ in FIG. 8 taken alongthe line A-A, and FIG. 9B is a cross-sectional view showing the spoolvalve 70 in FIG. 8 taken along the line B-B. In these drawings, the samereference symbols are applied to the equivalent elements included in thefirst embodiment. As shown in FIGS. 8, 9A, and 9B, the spool valve 70′is provided with additional connection ports H7′ and H8′, and the spoolvalve 70′ has two rows of connection ports arranged in theright-and-left direction in the drawings, each of which includes fourconnection ports. The spool valve 70′ is provided with two spools 71′and 72′ arranged in the right-and-left direction in the drawings. Thespool 71′ is made slidable to positions for making connection anddisconnection between the drain branching passage 38′ and the cylinderactivation passage 35. The spool 72′ is made slidable to positions formaking connection and disconnection between the cylinder activationpassage 35 and the supply branching passage 36′. In this embodiment, asin the first embodiment, even when the spool 43 of the spool valve 33 isfixed in the position shown in FIG. 6 due to defectiveness, the engine Ecan be reliably placed in or returned to the all-cylinder activationmode by operating the spools 71′ and 72′ of the spool valve 70′ as shownin FIGS. 9A and 9B.

INDUSTRIAL APPLICABILITY

As explained above, according to the cylinder operation controlapparatus of the present invention, because the internal combustionengine can be reliably returned to the all-cylinder activation mode froma state in which all of the cylinders are deactivated, an all-cylinderdeactivation operation, in which all of the cylinders are deactivated,may be executed; therefore, the engine friction can be greatly reduced,and thereby fuel economy can be improved.

According to another cylinder operation control apparatus of the presentinvention, the engine friction can be further reduced, and thereby fueleconomy can be further improved.

According to another cylinder operation control apparatus of the presentinvention, the operation oil can be supplied to the cylinder activationpassage so as to place the engine in the all-cylinder activation modeeven when the engine is supposed to be placed in the cylinderdeactivation mode in which the operation oil is supplied to the cylinderdeactivation passage by the operation of the switching device.Therefore, the internal combustion engine can be reliably returned tothe all-cylinder activation mode from a state in which all of thecylinders are deactivated, an all-cylinder deactivation operation, inwhich all of the cylinders are deactivated, may be executed.Accordingly, the engine friction can be greatly reduced, and therebyfuel economy can be improved.

According to another cylinder operation control apparatus of the presentinvention, the connection or disconnection between the supply branchingpassage and the cylinder activation passage, and the connection ordisconnection between the drain branching passage and the cylinderdeactivation passage can be executed by just a single operation;therefore, a preferable efficiency in operation can be obtained.

1. A cylinder operation control apparatus comprising: an internalcombustion engine which is adapted to operate in an all-cylinderactivation mode in which all-cylinders thereof are activated, and in acylinder deactivation mode in which at least a cylinder thereof isdeactivated; a lift amount changing device which is associated with theinternal combustion engine, and which enables switching between theall-cylinder activation mode and the cylinder deactivation mode bychanging the amount of lifts of intake and exhaust valves associatedwith the cylinders; a lift operating device which is associated with thelift amount changing device to operate the same; a cylinder activationenforcing device which is operatively disposed between the lift amountchanging device and the lift operating device so as to enforce theall-cylinder activation mode as necessary; and a control unit which isoperatively connected to the lift amount changing device, the liftoperating device, and the cylinder activation enforcing device, forcontrolling the operation mode of the internal combustion engine.
 2. Acylinder operation control apparatus according to claim 1, wherein thelift amount changing device comprises a hydraulic variable valve timingmechanism.
 3. A cylinder operation control apparatus according to claim2, wherein the control unit is adapted to control the oil pressure forthe hydraulic variable valve timing mechanism so as to suspend theoperations of the intake and exhaust valves when the internal combustionengine is placed in the cylinder deactivation mode.
 4. A cylinderoperation control apparatus according to claim 2, wherein the controlunit is adapted to operate the cylinder activation enforcing device soas to enforce normal operations of the intake and exhaust valves asnecessary.
 5. A cylinder operation control apparatus comprising: aninternal combustion engine which is adapted to operate in anall-cylinder activation mode in which all-cylinders thereof areactivated, and in a cylinder deactivation mode in which at least acylinder thereof is deactivated; a lift amount changing device which isassociated with the internal combustion engine, and which is adapted tochange the amount of lifts of intake and exhaust valves associated withthe cylinders using an operation oil supplied from a hydraulic powersource; a cylinder activation passage connected to the lift amountchanging device for placing the internal combustion engine in theall-cylinder activation mode; a cylinder deactivation passage connectedto the lift amount changing device for placing the internal combustionengine in the cylinder deactivation mode; an oil supply passage which isconnected to the cylinder activation passage and the cylinderdeactivation passage for supplying the operation oil to the lift amountchanging device, and which is provided with an oil supply branchingpassage branching therefrom; a drain passage which is connected to thecylinder activation passage and the cylinder deactivation passage forallowing the operation oil to return to the hydraulic power source, andwhich is provided with a drain branching passage branching therefrom; aswitching device which is connected to the cylinder activation passage,the cylinder deactivation passage, the oil supply passage, and the drainpassage, for optionally supplying the operation oil from the hydraulicpower source to the cylinder activation passage or to the cylinderdeactivation passage; and a cylinder activation enforcing device whichis connected to the cylinder activation passage, the cylinderdeactivation passage, the oil supply branching passage, and the drainbranching passage, for enforcing the all-cylinder activation mode.
 6. Acylinder operation control apparatus according to claim 5, wherein thecylinder activation enforcing device comprises: a cylinder activationport for optionally connecting the oil supply branching passage to thecylinder activation passage or disconnecting the oil supply branchingpassage from the cylinder activation passage; and a cylinderdeactivation port for optionally connecting the drain branching passageto the cylinder deactivation passage or disconnecting the drainbranching passage from the cylinder deactivation passage.
 7. A cylinderoperation control apparatus according to claim 6, wherein the cylinderactivation enforcing device comprises a spool valve having a spooltherein, the spool valve being adapted to perform the connecting anddisconnecting operations between the oil supply branching passage andthe cylinder activation passage, and connecting and disconnectingoperations between the drain branching passage and the cylinderdeactivation passage, by sliding the spool to respective predeterminedpositions.